Her husband, a prominent Kuwaiti citizen, was murdered by Islamic extremists for condemning the terrorist attacks of September 11, and now, she says in her hastily typed e-mail, those same extremists are out to kill her.

The situation is desperate, but you can help. All Mohamed asks is a letter of invitation so she can obtain a U.S. visa and your bank-account number so she can move the $40 million her husband secretly bequeathed her to the United States. For these kindnesses, she will repay you with 15 percent of her fortune. Please reply to her Yahoo.com e-mail address with "your most confidential telephone numbers" for further instructions.

Sound like the easiest $6 million you'll ever make? Think again. According to the U.S. State Department, succumbing to such a plea could cost you everything you own, possibly even your life.

"Mrs. Mary Mohamed" is actually a professional con man -- a member, most likely, of one of any number of international crime rings operated by Nigerian nationals inside and outside their home country, where financial fraud has burgeoned into a multibillion-dollar industry over the past decade. Far from having a fortune to share with you, the perpetrators are after your own hard-earned cash, which they will demand in the form of "good-faith money" or advance fees to secure the release of the supposedly sequestered funds. And they will go to almost any lengths to get it.

Known to law enforcement as the "Nigerian Advance-Fee Fraud" or "419 Scam" ("419" being the applicable section of the country's criminal code), the Secret Service terms the phenomenon a "growing epidemic," and according to the Postal Service, it is accountable for losses of more than $100 million a year to American citizens alone. There are countless variants, but the opening play is always the same: a "confidential" message purporting to come from a high government official, businessman or other VIP, followed by elaborate "proofs" of legitimacy calculated to gain victims' confidence and part them from their money. Individual losses to U.S. citizens have ranged from a few thousand dollars to a million bucks.

Victims -- particularly those naive enough to travel to Africa to consummate such deals or try to recover their losses -- also report being subjected to extortion attempts, intimidation and violence at the hands of 419 scammers says the Secret Service agent I spoke with (who asked not to be named). Just last December, the Helsinki newspaper "Helsingin Sanomat" reported that a Finnish businessman was kidnapped, beaten and held for ransom by a Nigerian crime ring operating in South Africa after they had already bilked him of hundreds of thousands of dollars in "advance fees." At least 15 people are known to have been murdered in connection with these scams since the early 1990s.

It may seem unlikely that anyone would actually fall for such schemes, but according to the Secret Service official, about 1 percent of those solicited do. The reasons are mainly psychological. For one, practitioners of advance-fee fraud, like all con artists, can be extraordinarily persuasive and persistent. But criminologists say the victims, too, share certain personality traits that increase their susceptibility. Greed and gullibility obviously figure in, as do such tendencies as being a risk taker, succumbing easily to flattery or intimidation and failing to take an interest in news and current events. Sometimes the victims have a criminal bent themselves.

Demographics play no role at all, said the same official. Unlike other types of fraud, in which perpetrators target particular groups such as the elderly or the well-to-do, 419 scammers take a scattershot approach, soliciting anyone and everyone.

The Internet has exacerbated the problem. "Nigerian Money Offers" zoomed from the seventh to the third most common type of online fraud last year according to the Web site Internet Fraud Watch, and the reason is obvious. In days gone by, the scammers had to canvass potential victims one at a time by fax and snail mail; now they have the speed, cost-effectiveness and anonymity of the Internet at their disposal, and they're taking full advantage. They ply their trade in Internet cafés, switching identities with the click of a button using easily obtainable Web e-mail accounts and spamming their elaborate come-ons to thousands of harvested e-mail addresses at once. Though only a tiny percentage of recipients reply, in doing so they identify themselves as easy marks, inviting further contact and the inevitable pressure tactics from the e-grifters.

The Secret Service Web site says the agency has drastically stepped up its efforts to apprehend and prosecute 419 scammers in recent years -- even to the extent of establishing a presence in Nigeria itself -- but its increased successes have been counterbalanced by an explosion in the rate of new cases. The obstacles to fighting the scam are many, says the agent I spoke with, not least the reluctance of embarrassed and fearful victims to come forward and press charges. Also hampering enforcement efforts are the dispersion of the crime rings to far-flung countries and their increasing reliance on the Internet. While prosecutions remain infrequent as compared to the number of reported crimes, the Secret Service touts a higher success rate now than at any time in the past, mainly due to the cooperative efforts of law-enforcement agencies internationally, including the Nigerian national police force.

Still, officials place their main emphasis on prevention, through increased public awareness and education. The State Department, the Secret Service, the Federal Trade Commission and the FBI all maintain informational Web pages devoted specifically to 419 fraud.

What should you do if you receive an e-mail you suspect is a scam? First, and most important, do not reply to it. Simply delete the message -- or, alternatively, contribute it to the Secret Service's database by forwarding it to 419.fcd@usss.treas.gov -- then delete it.

If you're unsure whether a message you've received is a scam, here are a few dead giveaways. The message:

* has a header that reads "URGENT AND CONFIDENTIAL" or "BUSINESS PROPOSAL" or "URGENT ASSISTANCE," etc. * purports to originate from a high government official, oil executive or banker (or relative of same) in a foreign country. * promises a substantial percentage of a huge sum of money. * requests personal information such as your address, telephone number or bank-account data. * sounds too good to be true.

If you have already been victimized and have suffered a financial loss at the hands of 419 scammers, contact the Secret Service immediately, advises the U.S. Commerce Department's Nigeria officer (who asked not to be named). You can find the number of the field office nearest you by checking the government pages of your telephone book.

The Commerce official also advises taking immediate steps to prevent the scammers from taking further advantage of you: "Carefully review any personal information you've given them. Change bank-account numbers, phone numbers -- anything they may have had access to."

One thing you should not do is expect to ever see your money again. Recoveries are even rarer than prosecutions. "In four years, I've never seen it happen," says the official, who listens to victims' horror stories daily.

But for those who've been taken in by the 419 scam, there is one small solace: At least you know you're not alone.